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Re: [Xen-devel] [Xen-users] VGA passthough still not working

On Wed, 2012-01-25 at 03:26 -0500, Likarpenkov Alexander wrote:
>  DM> I use the xl toolstack, not xm.  I don't think xm is being
> actively
>  DM> maintained, at least not for current releases.
> You can in a nutshell what better xl xm?

I'm not the person who can give you the most thorough response, however,
I can tell you what i know.  Xl is lighter-weight (C vs python, among
other structural differences).  Xl is the only 'suuported' toolstack
going forward, and xend/xm is no longer being maintained.  AFAICT, xl is
near feature parity with xend/xm in the current unstable.

Xl is the way to go if you're working on xen-unstable.

I imagine users on 4.1.x are encouraged to use it, but certain features
(such as recognizing and passing gfx_passthru flag to qemu) may or may
not be implemented in older versions, so for your testing, you may have
to use xm for some commands if you're building an older Xen.

If anyone can clear that up/correct any innacuracies, please jump in.
There should probably be a wiki page on this if there isn't already one.
Looked just now, and the only relevant info seems to be here:

>  DM> I don't know what a video could show you.  In the ATI case,
> there's no
>  DM> signal until Windows loads the drivers.  It automatically
> disables the
>  DM> emulated adapter, so i can watch the BIOS and Windows loading
> screens
>  DM> via VNC, then my desktop appears on the monitor and the VNC
> console
>  DM> goes black.
> I say that ATI produces the same effect. I do not see anything until
> the
> welcome screen and only when gfx_passthru = 0. If gfx_passthru = 1 -
> qemu
> shell on vnc console and freezed domU :(

You won't be able to passthrough an ATI card with the BIOS for multiple
reasons.  First, the ati bios keeps a copy of the pci config space, so
certain values need to be modified for it to work properly with the
guest addresses.  The most recent experimental patch for this was from
december 2010:
I can confirmm i had limited success with this.

However, this patch was based on xen-unstable before the 4.1-rc's came
out.  You can try building an older version of xen (in that thread, i
mentioned the specific C/S i used in testing) and applying the patch or
forward porting the patch to the current xen/qemu-xen.

Also, i believe you said the card you're trying to pass through is not
the primary card in your host system.  If that's the case, don't use
gfx_passthru or expect to get the video bios working.  The 'primary'
video adapter owns certain io ports and memory areas that are consitent
from machine to machine.  Also, the system will copy the vbios from the
card to a location in memory (0xc0000) so it can execute at boot time. 

Xen's gfx_passthru code depends on all of these factors.  As the code
stands, if you use gfx_passthru on a secondary card, it will still copy
the vbios from the primary card (as it simply reads memory from
0xc0000), and directly map io ports and low memory areas to those used
by the primary card in the host system.  In this case the guest will
almost certainly never get past executing ROMBIOS, and the host may or
may not lock up or experience 'issues'.

>  DM> In the IGD case, i can see the output from ROMBIOS and the
> windows
>  DM> loader (or grub2) on the monitor.  If i'm booting a XP domU, the
>  DM> windows login screen then appears.  If i'm booting a Win7 domU,
> the
>  DM> screen goes black.  If i'm booting a fedora16 domu, the signal
> vanishes
>  DM> entirely. In the Win7 case, the domU seems to be stuck in a loop.
> In
>  DM> the Fedora case, i can ssh to the machine and see various WARN_ON
> dumps
>  DM> in dmesg related to the i915 driver, and eventually, a message
> saying
>  DM> it failed to reset the adapter.
>  DM> I think that gives you more detail than any video i could post.
> Yes, your post is really better video

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